1. Field of the Invention
The present invention relates to an improved process for the preparation of at least double metal silicates from solutions of alkali metal silicates. The invention also relates to the products of such process and the uses thereof, especially in the manufacture of glass.
2. Description of the Prior Art
It has long been known to this art to prepare precipitated silicas by the action (acidulation) of an acidification agent, such as an organic or inorganic acid, on a silicate. It is also known to prepare simple or double silicates by double decomposition.
However, a number of problems give rise to serious difficulties both in regard to the resultant product and in regard to the process itself. Of such difficulties, resultant purity, granulometry and density of the product, and ease of operation, selection of the materials used and energy savings with respect to the process, are representative, and not intended to be exhaustive.
Thus, in the case of glass making, for example, and although this is a method which has been carried out for a very long period of time, the compositions employed therefor are produced by melting the various ingredients, which, besides the ensuing problems as regards energy and operation due to the use of high temperatures over a prolonged operating period, gives rise to serious problems with respect to controlling the glass-making formulations, and in particular the homogeneity thereof.
And it has long been proposed, in British Patent Specification No. 512,292, to avoid the solid powder form of the constituents of the glass making admixture, but rather to precipitate same from solution, by means of suitable chemical process, in order to reduce the melting temperature and to achieve a reduction in the time required for melting.
Unfortunately, however, such a precipitation suffers a priori from the difficulties which ensue, on the one hand from elimination of by-products, and on the other from the necessity to evaporate large amounts of water.
In European Patent Application No. 80/400197.2, filed Feb. 8, 1980, and assigned to the assignee hereof, another process has been proposed which employs reactants in solution form, wherein, utilizing a solution of a soluble alkali metal silicate, at least partial substitution by at least one oxide of another metal is effected.
From a practical point of view, this process is conducted using solutions of sodium and/or potassium, and the attack operation is effected by means of a metal nitrate which can be produced by metal attack or dissolution of the metal oxide or hydroxide by nitric acid. This results in an amorphous and isotropic composition which is exceedingly interesting from a technical standpoint; nonetheless, the process suffers from the disadvantage of entailing preparation of the various metal silicates involved in the composition, thus likely giving rise to energy requirements which will not be inconsiderable.
Further compare, generally, U.S. Pat. No. 2,386,337; French Pat. Nos. 844,113, 853,480 and 2,011,819; and Chemical Abstracts, 53, 18418d (1959).